Our sky is filled by millions of stars, all varying in size, colour, magnitude and distance. Early travellers used the stars as a navigational tool relying on the knowledge of time and position to guide them across the land and oceans.
Early astronomers could see pictures formed by the stars, often used to depict scenes from 48 classic Greek legends and Mythical stories. A total of 88 constellations are recognised by the International Astronomical Union. The constellations are used to recognise different sections of the sky and help name the stars in those groups. The Greek alphabet is used to nominate each star according to magnitude or brightness, alpha being the brightest and beta being the second brightest and so on.
Using the constellation Centaurus as an example, the brightest star is named Alpha Centauri with the next brightest Beta Centauri etc. In some constellations an object such as a globular cluster or nebula may be included in the Greek list. (Notice that the Genitive version of the Name is used). This system was devised by Johann Bayer. Even as recently as the 1930, Constellation boundaries have been changed which confuses the sequence of stars in the constellation and their Greek name order.
Twelve of the 88 constellations are known as Zodiac constellations. The Zodiac constellations are all found on the Elliptic being the path that the Sun, Moon and Planets travel across the sky. These constellations have been common place names representing the horoscope constellations used by Astrologists.
Some of the constellations are not visible from the southern hemisphere and some not visible from the northern hemisphere. As Astronomy was first documented in the Northern Hemisphere, many of the characters and images drawn to represent the constellation have been seen from the northern aspect. If you are viewing these from the southern hemisphere, the image will appear upside down. It can also be said that the further north you are, the elliptic is further to the south, not over head. This emphasises the pictorial image as seen by the original astronomers where the image is standing up and not on its side such as viewed directly overhead. Remember, not every star or object is named by a Greek letter, some have catalogue names or numbers such as M45 or NGC1336
You can view detailed information about each Constellation here: http://www.shoalhavenastronomers.asn.au/constellations/